The energy crisis caused a considerable growth of interest in alternative sources of energy in the past few years. Among the several energy sources being explored, wind energy, which is a form of solar energy, became a significant energy source. If the efficiency of a windmill can be increased, the cost of wind energy will be reduced together with the dependency on expensive, polluting power generators.
There are two types or configurations of windmills used for wind power generation: horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT). HAWTs spin on a horizontal axis and are the more common design of the two turbine designs. However, HAWTs are not as efficient as VAWTs because they must be adjusted so that their blades can capture the wind. In contrast, VAWTs, which spin on a vertical axis, can capture wind regardless of the direction it is blowing, and therefore can process wind energy more efficiently. Furthermore, generators and gearboxes for the VAWTs can be placed on the ground, which makes them much more accessible for maintenance.
As shown in FIGS. 1A, 2A, and 3A, there are existing VAWT designs, such as the design described in U.S. Pat. No. 7,084,523 to Noguchi (“Noguchi”). However, these VAWT designs are based on the Bernoulli principle and suffer from several inefficiencies. Bernoulli's principle relies on the asymmetrical shape of an airfoil to cause air to flow over the top and bottom surfaces of the airfoil at different speeds. The variations in speeds result in different pressures at the top and bottom surfaces of the airfoil, which induces varying forces such as lift, as shown in FIG. 1A. Bernoulli-based designs, such as Noguchi, rely on this induced lift component to increase forward momentum of the blades in perpetuity. For example, Noguchi repeatedly states that the blade should have a “high lift coefficient”. Furthermore, Noguchi attaches its blades to the main shaft at a slight angle 201 from the plane of rotation, 202, as shown in FIG. 2A. This offset induces additional lift that can be used to drive the blades.
While a component of the induced lift does help propel the blades, it also creates a significant number of other problems. For example, there is an outward component of the induced lift that is orthogonal to, and away from, the center of rotation. This orthogonal component pulls the blades away from the center, which causes the blades to try to “lift off” from the center of rotation as shown in FIG. 3A, and creates significant resistance thereby slowing down rotation. The orthogonal lift component also creates stresses on the blades and friction between the bearings and shaft, by constantly pulling the blades outward during rotation. This increased resistance and stress caused by the asymmetrical shape of Noguchi and other Bernoulli-based designs significantly decreases the performance, and the life, and of the windmill.
The shape of windmill blades highly influences their rotation and energy conversion efficiency. As a new generation of companies are now developing on a VAWT platform, there is a need for an optimum blade shape that can increase the overall efficiency and productivity of the windmill, resulting in a lower cost per kilo-watt hour of energy produced.